A comparative study of drought characteristics using meteorological drought indices over the central main Ethiopian Rift

Abstract

Droughts are defined by a prolonged absence of moisture. For making drought assessments, a drought index is a crucial tool. This study aims to compare drought characteristics across the Central Main Ethiopian Rift using three drought indices – the Standardized Precipitation Index (SPI), the Reconnaissance Drought Index (RDI), and the Standardized Precipitation Evapotranspiration Index (SPEI) – from 1980 to 2017 at six climate sites in spring, summer, and a 6-month period (March - August). With 1% and 5% significance levels, Modified Mann-Kendall and Sen’s Slope Estimators were used to determine trend and magnitude, respectively. The temporal fluctuations of the three drought indices revealed that droughts are frequent, unpredictable, and random. Furthermore, they behaved similarly and had significant links. At most places, the drought indices found no significant trends. However, in the spring season, Butajira (by the three indices) and Wulbareg (by the SPI) showed significantly decreasing trends (increasing drought severity), with change rates ranging from -0.03 to -0.04/year. A comparison of drought characteristics revealed that droughts have become more severe and frequent in recent decades, with spring being more common than summer. This study, which employed a variety of drought indices, could assist water resource planners better understand drought events.